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Pyloric stenosis — MRCPCH FOP MCQ

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ModerateGastroenterologyPyloric stenosisMRCPCH FOP

A 5-week-old boy has progressive projectile non-bilious vomiting and persistent hunger. Blood gas shows pH 7.52, chloride 88 mmol/L and potassium 3.0 mmol/L. What is the most likely cause?

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Correct answer: E — Gastric outlet obstruction causing hypochloraemic metabolic alkalosis

Projectile non-bilious vomiting in a hungry 5-week-old with hypochloraemic hypokalaemic metabolic alkalosis is classic for pyloric stenosis. Volvulus typically causes bilious vomiting and is a surgical emergency with a different pattern. Viral gastroenteritis more often causes diarrhoea and metabolic acidosis from dehydration. The pearl is to correct fluid and electrolyte abnormalities before pyloromyotomy.

Reference: NICE CKS Vomiting in children; Paediatric surgery guidance